Cassini uvis observations of Saturns rings

Abstract

The Cassini Ultra-violet Imaging Spectrograph (UVIS) is part of the remote sensing payload of the Cassini Orbiter spacecraft. Its science objectives include investigation of the chemistry, clouds, and energy balance of the Titan and Saturn atmospheres ; neutrals in the magnetosphere ; D/H ratio for Titan and Saturn ; and structure and evolution of Saturns rings. The UVIS has two spectrographic channels which provide images and spectra covering the ranges from 56–118 nm and 110–190 nm. A third optical path with a solar blind CsI photocathode is used for high signal to noise ratio stellar occultations by rings and atmospheres. A separate hydrogen-deuterium absorption cell (HDAC) measures the relative abundance D/H from their Lyman-alpha emission. The rings of Saturn are the best-studied of planetary rings and contain the majority of the ring material in the solar system. The four-year Cassini tour provides multiple observation opportunities and long time coverage. The UVIS observations include photometry, imaging, spectroscopy, and stellar occultations. Numerous diffraction-limited star occultations by the rings are a prime objective for the UVIS. The 2 ms integration period in this mode will give a ring radial resolution of better than 20 m. The counting rate is 50 × greater than the Voyager star occultations in a resolution element 5 × smaller. Multiple opportunities on the same Saturn passage will define temporal and azimuthal variation. We expect to observe waves, wakes and ring edges—all characteristics of ring dynamics and history. The imaging resolution is 1 mrad, or 1000 km from a viewing range of 10 6 km. The UVIS is sensitive to the shortest wavelengths of all the remote sensing experiments, and thus the scattered light from the smallest ring particles. In combination with images from ISS and VIMS, CIRS spectra, and